lua - Corona SDK(LUA) - 尝试调用 upvalue 'spawnEnemy'(零值)

Question

我只是想将 eventListener 添加到一个对象，当我点击它时它应该消失。但我收到标题中提到的错误。这是我此时的完整代码:

-- housekeeping stuff

display.setStatusBar(display.HiddenStatusBar)

local centerX = display.contentCenterX
local centerY = display.contentCenterY

-- set up forward references

local spawnEnemy

-- preload audio

-- create play screens

local function createPlayScreen()

    local bg = display.newImage("background.png")
    bg.y = 130
    bg.x = 100
    bg.alpha = 0

    local planet = display.newImage("planet.png")
    planet.x = centerX
    planet.y = display.contentHeight +60
    planet.alpha = 0

    transition.to( bg,  { time = 2000, alpha = 1,  y = centerY, x = centerX } )

    local function showTitle()
        local gametitle = display.newImage("gametitle.png")
        gametitle.alpha = 0
        gametitle:scale (4, 4)
        transition.to( gametitle, { time = 500, alpha = 1, xScale = 1, yScale = 1 })
        spawnEnemy()
    end 
    transition.to( planet,  { time = 2000, alpha = 1,  y = centerY, onComplete = showTitle } )
end

-- game functions

local function shipSmash(event)

    local obj = event.target
    display.remove( obj )

end

local function spawnEnemy()

    local enemy = display.newImage("beetleship.png")
    enemy.x = math.random(20, display.contentWidth - 20)
    enemy.y = math.random(20, display.contentHeight - 20)
    enemy:addEventListener ( "tap", shipSmash )

end


local function startGame()

end


local function planetDamage()

end


local function hitPlanet(obj)

end




createPlayScreen()
startGame()

这是错误窗口的样子:

我在这个领域有点新(LUA编程)，所以很抱歉可能是愚蠢的语法错误或其他什么，但我看到的是，在我编写这行代码后，这个错误出现了: enemy:addEventListener ( “点击”，shipSmash)

Answer 1

将本地函数spawnEnemy()更改为函数spawnEnemy()，因为该变量之前已声明。是的，这是初学者典型的 Lua 陷阱。